DTIC ADA171385: Biological Applications and Effects of Optical Masers.

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BIOLOGICAL APPLICATIONS AND EFFECTS OF OPTICAL HASERS
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BIOLOGICAL APPLICATIONS AND EFFECTS OF OPTICAL MASERS

Annual Report

March 15, 1983 - March 15, 1984
June 1984

William T. Ham, Jr., Ph.D.

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(U) Biological Applications and Effects of Optical Masers

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William T. Ham, Jr., Ph.D.

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Table of Contents

1.

Abstract

Page

1-3

2.

Argon/krypton Acoustically Nodulated Laser

Page

4-5

3.

Hinieue Radiant Exposures for 40 ps Pulses of 647 ne Light.

Page

5-7

4.

Additivity and Reparation froe Repetative Exposures to

Short Wavelength Light.

Page

7-10

5.

Histological Analysis of Photocheeical Lesions Produced Under
Conditions of Elevated Blood Oxygen.

Page

10-12

6.

Basic Mechanises Underlying the Production of Photocheeical

Lesions in the Maeealian Retina.

Page

12-13

7.

Long-Tere Repetitive Exposures of Trained Monkeys to Near

UV Radiation and Short Wavelength Light.

a. Near UV effects an lens Mith noreal and dilated pupil.

b. Blue light effects on the retina.

c. Near UV phototoxicity in the aphakic prieate retina.

Page

13-16

8.

Publications, Recent and In Press, Abstracts.

Page

16-17

9.

Additional Activities.

Page

17—18

10.

Reprints of Publications and Abstracts.

1

1. Abstract

(2) The argon/krypton laser was back in operation in October
1983 after eany vicissitudes during the fiscal year.
Unfortunately, the Bragg cell that drives the acoustic Modulator
failed to function. The argon/krypton laser and acoustic
■odulator are operating satisfactory now with a Bragg cell on
loan by Spectra-Physics while our Bragg cell has been sent to
California for repairs. The research on threshold data as a
function of wavelength and Modulation frequency can now proceed.
(3) Additional data on 40 |ls pulses at a PRF of 400 Hz are
presented in Table I. Figure 1 gives a log-log plot of threshold
corneal power Pc vs exposure tiae in s for PRF's of 100, 200 and
400 Hz. Pc decreases with PRF for shorter exposure tiaes but
seeas to converge far exposures greater than 1000 s. (4) A
Workshop dealing with the possible long-tera ocular effects of
optical radiation on aging and aacular degeneration is discussed
and a final draft of the report of the Working 6roup assessing
light effects on the retinal pigaent epitheliua (RPE) is appended
to this report. A preliainary experiaent on the additivity and
reparation of repetitive exposures of light to the saae retinal
site is described. Repetitive 100 s exposures of blue light (440
nm rt 5 na) at 24 hour intervals were found to be additive for 2
exposures at SOX of threshold, for 3 exposures at 40X of
threshold, and for 4 exposures at 30X of threshold. Wavelengths
at 490 and 520 na were not additive even at 50X of threshold.

4

2

(5) Two aacaque Monkeys were used to study the histological
consequences of retinal blue light lesions produced under high
arterial blood oxygen tension. Analysis of the various photic
lesions showed only Moderate daeage to the neural retina but very
extensive daaage to the RPE. This is the histopathological
pattern of a typical blue light lesion shown in previous studies
but aore severe and appearing earlier after exposure. A report
of this research is "in press" in Invest. Ophthalaol. & Vis. Sci.

A preprint is enclosed. (6) The enhanceaent of retinal
sensitivity to blue light daeage when the aniaal is highly
oxygenated (threshold lowered by a factor of 3 at arterial P0» of
270 mm of Hg) suggests but does not prove that 0a free radicals
and sensitized Molecules (05, Ha0a, 0H-,‘0a> play an iaportant
role in photocheaical daeage to the retina. Beta-carotene
provided protection froa blue light daaage plus oxygenation in
the only aniaal tested so far. Results to date do not contradict
the hypothesis that photodynaMical action (probably singlet
oxygen) is a contributing factor leading to photocheaical lesions
in the retina. A report describing these effects is published in
Curr. Eye Res., reprint enclosed. (7) Two trained aonkeys, one
with noraal pupil size, one with pupils dilated > 8 aa, have
undergone 950 and 366 daily exposures respectively to the
spectrua 330-420 na (5aW*ca“a at cornea). As yet, no lenticular
abnoraal i ti es have heen detected in either aniaal. Another
trained aniaal with daily exposures to the spectrua 330-490 na

3

developed a f unduscopical 1 y visible lesion. This anieal was
recently sacrificed for histological analysis of the lesion. A
trained aphakic eonkey showed extensive retinal daaage after 316
daily exposures to the spectrue 330-420 na. The retinal
irradiance during an exposure was approxiaately 1 aM*ca~3, a
figure soaewhat less than that to be expected on the retina of an
aphakic huaan eye on a bright sunny day between noon and 2 p.a.
This aniaal has been sacrificed. Histological analysis showed
widespread RPE abnoraal i ti es in the superior and nasal
paraaacular fundus. This experiaent deaonstrates that the RPE in
an aphakic eye can be daaaged by saall daily exposures to near UV
radiation.

This has been a year of frustration in our attempts to
investigate ainiaua radiant exposures for acoustically aodulated
wavelengths at 647na and 488n* as provided by the argon/krypton
laser. The program, as originally planned, called for a
comparison of threshold data at these two wavelengths as a
function of Modulation frequencies 1,10 and 100 kHz and 1, 10 and
20 HHz. Our first problea was the argon/krypton laser; we were
unable to aake it oscillate. Spectra-Physics does not renovate
old tubes but offered to sell us a new tube for $7,700 including
shipping charges if we would ship the old laser to thea. In an
effort to save funds we opened negotiations with Phoenix Lasers,
Ltd. who offered to renovate the old laser for a price ranging
froa $200 to $5,200 depending on the reason for the Malfunction.
The argon/krypton laser was shipped to thea on July & 1983. Mhen
it arrived in Palo Alto, California, Phoenix Lasers, Ltd. had
gone out of business. Me were able to arrange for the delivery
of the laser to Spectra-Physics in Mountain View, California.
They repaired and shipped it back to us in October 1983. But our
troubles had only begun. The acoustic Modulator, a coaplicated
electro-optical device, was defective. For the next two months
we tried a nuaber of ways to correct the fault as suggested by
the engineers at the New Jersey plant of Spectra-Physics. The
aajor problea is that this type of acoustic aodulator is obsolete

6

* y r* wk » v

Table I

Radiant Exposures Hp per

pulse and

He total in J*ca~a

for a

ainiaal

lesion in the aonkey retina are

given for 40 ps pulses at |

pulse

repetition frequencies

(PRF ) of

100, 200, and 400

pulses

per s

for exposure durations ranging

froa 1 to 3000 s.

Eo in

W-ce-*

on the retina is calculated on the assuaption that the 1

I l„.r

beaa produced 25 pa

lesions

at the 1/e points

of the 1

r

{ Gaussian distribution, E*E0

exp (-r*/2

O*) according to the

■! for aula

Eo=P«T-<2 O*)-* where P« in M

is the power entering the

1 cornea

as aeasured, T is

the transaission through the

ocular I

[

j eedia

(0.93 for 647na)

and i s

the Gaussian paraaeter 1

*

|j corresponding to a radius r of

12.5 pa.

•

Exposure Tiae

Nuaber P„

Eo H

o per pulse H0

additive

s

Pulses U

H-ca~*

aJ'ca"*

J • ca~*

•

1

1x10* .14

265.

10.6

1.06

1

2x10* .082

155.

6.22

1.24

1

4x10* .052

98.7

3.95

1.58

10

1x10* .080

152.

6.06

6.06

10

2x10* .059

113.

4.51

9.02

10

4x10* .039

74.7

2.99

11.9

10*

lx 104 .029

54.9

2.19

21.9

' 10*

2x 104 .031

58.7

2.35

47.0

10*

4xl04 .021

39.4

1.58

63. 1

| 10*

1x10" .014

26.5

1.06

106

I 10*

2x10" .012

22.7

0.91

182

10*

4x10* .010

19.0

0.76

305

3x10*

3x10* .0067

12.8

0.51

153

3x10*

6x10* .0065

12.2

0.49

293

3x10*

12x10* .0054

10.0

0.41

494

1

7

g w |«»|u «.

In Figure 1 Me have plotted the corneal poMer Pe entering
the eye in W against exposure duration in s as shoMn in Table I.

This is a log-log plot, The circles represent a PRF of 100 Hz,
the x's 200 Hz and the inverted v's 400 Hz. It can be seen that
Pe decreases Mith PRF for the shorter exposure durations but
seees to converge as the exposure duration is extended beyond
1000 s. It seees logical to suppose that as the tiee between
pulses decreases froa 10 eilliseconds to 2.5 ailliseconds the
additivity between pulses increases. Based on a thereal eodel
this would mean temperature additivity as the tiee between pulses
decreases. For high PRF's the pulse eodel should approach the CW
condition. Spot size on the retina is an important factor. For
very small spot sizes like those produced by lasers, as in this
experiment , the tiee required to reach temperature equilibrium is
very short z: microseconds and the irradiances are high. Small
spot size also means rapid dissipation of energy when the pulse
is over, so that for low PRF’s one would not expect temperature
additivity.

4. Additivity and Reparation from Repetitive Exposures to Short Wavelength Light.

Interest is increasing in the possible effects of long-term
chronic exposure to sunlight and man-made optical sources. For
example, Dr. Han attended a Workshop on Long-Term Visual Health
and Optical Radiation sponsored by the Division of Risk
Assessenent, National Center for Devices and Radiological Health,
Food and Drug Administration. This Workshop was co-sponsored by

5*5

the Army Medical Research and Development Coeeand, the Lawrence
Berkeley Laboratory, Department of Energy and the Occupational
Safety and Health Adainistration. The Coaaittee on Vision,
NAS-NRC was a participating organization. Leading questions
posed by the Workshop concerned the effects of daily, chronic
exposure to short wavelength light on aging and degeneration of
the retina and lens leading to degenerative aaculopathies and
senile cataract. Dr. Has chaired the Working 6roup assigned the
task of assessing light daaage to the RPE and its possible
relationship to aging and aacular degeneration of the retina. A
preprint of the final draft subaitted by the RPE Working Group is
attached to this progress report. It is scheduled to be
published by CRC Press in June 198S.

We have begun an investigation on the additivity and
reparation of repetitive exposures of light to the saae retinal
site. Originally we intended to use repetitive exposures to the
saae retinal site at 24 hour intervals for light levels SOZ, 40Z,
30Z, 20Z and 10 Z of threshold at 3 wavelengths of 440, 490, and
520 na. We planned to use a 500 jja spot size and exposure tiaes
of 100 s. The protocol called for 15 exposures across the retina
in 3 rows with 5 different exposure levels at each wavelength in
a single eye. Each location would be carefully documented by
fundus photography. The plan was to anesthetise the aniaal on a
daily basis for 21 days including Saturdays and Sundays. We have
completed the initial step of this protocol by exposing one

10

aniaal for a 5 day period using 20 na filters peaked at 440, 490

and 520 na as provided by the 2500 M xenon laap with quartz

optics. Five exposures at 50, 40, 30, 20 and 10 percent of a
predeterained threshold Mere given at each of these wavelengths.
After 5 daily exposures, 3 lesions Mere detectable at the 440 na
Mavelength; that is 50% of threshold shoMed up as a lesion on the
third day, 40% on the fourth day and 30% on the fifth day. No
lesions appeared, even on the fifth day for the longer

aavelengths 490 and 520 na. This experiaent deaonstrates the

sharp rise in retinal sensitivity to daaage as the Mavelength
decreases toNard the near ultraviolet. He estiaate a factor of
froa 3-5 for retinal sensitivity at 440 na as coapared Mith 4B8
na. Me plan to redesign the protocol for this experiaent at the
longer aavelengths 490 and 520 na. It probably Mill be necessary
to use 90, B0, 70, 60, and 50 percent of threshold for these

Mavelengths.

5. Histploflic^) Analysis of Phptpchepicaji l,qsi.afls.. P.rqdMfipl
Under Conditions of Elevated Blood oxvaen.

This study Mas perforaed on 2 aacaque aonkeys using the 2500

M xenon optical systea as radiation source for a narrow

bandwidth, 440 i- 5 na. Retinal iaage size Mas 1 aa and radiant

exposures to the retina ranged froa 36 to 11 J*ca~*. Oxygenation

Mas accoaplished under anesthesia by an endotracheal tube

i connected to a non-rebreathi ng apparatus equipped with separate

inhalation and exhalation valves Mith attached gas bag that Mas

i kept slightly above ataospheric pressure with a needle valve

i

)

11

regulator. A previously prepared tank eixture with an 80/20
ratio of 0a/Na was used. Arterial (feeoral) blood saeples were
taken before oxygenation began and after 30 einutes of breathing
the 80/20 eixture. Blue light exposures were perforaed
iaaediately after 30 einutes of oxygenation. Threshold data on
each anieal had been predetereined at least a week before the
oxygenation studies.

When blood oxygenation is not experieental ly elevated the
threshold radiant exposure for a blue light lesion to be
funduscopically visible at 2 days postexposure is about 30
J*ca~*. At a high blood P0a level (270 ea Hg) a radiant exposure
of only 11 J-ce~a gives a funduscopically visible lesion at 1 day
post exposure. This large increase in retinal sensitivity to
blue light daaage is probably due to photodynaeic action and aay
involve singlet oxygen though this reaains to be proved.
Analysis of the various photic lesions showed only aoderate
daaage to the neural retina but a strong response was seen in the
RPE. This is the histopathological pattern of a typical blue
light lesion shown in previous studies but sore severe. The
effect of elevated blood 0a is to increase retinal sensitivity to
photic daaage, to lower the daaage threshold and the tiae of its
appearance, and to increase the severity of daaage at a given
radiant exposure. Mild lesions observed at 23 and 57 days after
exposure show reaarkable recovery. A paper describing this
research has been accepted for publication by Investigative

12

Ophthalmology and Visual Science. A preprint is enclosed Mith
this annual progress report.

6. Basic Mechanises Underlying the Production of Photocheei cal
Lesions in the Mammalian Retina.

Dr. Hae delivered an invited paper Mith the above title at
an International Syaposiua on Light and Oxygen Effects on the Eye
sponsored by the Departaent of Ophthalmology, University of
Maryland School of Medicine. This paper has been published in
Current Eye Research. A reprint is enclosed in this annual
progress report.

Briefly, me have pointed out that the mammalian retina is
unique among body tissues because it is the only tissue Mhere
light is focused continuously on a group of cells that is highly
oxygenated, i.e. the retinal pigment epithelium (RPE) and the
photoreceptor cells that are among the most aetabol ical 1 y active
cells in the body. Both light and oxygen can be individually
toxic to cells. In combination toxicity should be enhanced. He
have shomn in the rhesus monkey that mhen the arterial blood
oxygen is enhanced to a P02 of 270 mm Hg, the threshold for the
blue light lesion is reduced by a factor of 3, from 30 J*cm~a to
10 J*ca~a. This implies photodynamic action and probably
involves singlet oxygen. Homever, this remains to be proved.
From a practical standpoint the retina of a patient undergoing
ophthalmic surgery, e.g. lens extraction, vitrectomy, etc., Mould
be more sensitive to retinal light damage if breathing oxygen.
Injections of methylprednisolone (125 mg i.v.) one hour before

exposure of the aacaque retina to blue light seeaed to provide

soae protection. However, ao re recent experiaents have not

substantiated this effect and we believe that auch aore research

is needed before the role of steroids in light daaage can be

assessed. The carotenoid B-carotene has been shown to provide

protection froa blue light daaage in one aonkey. This is further

evidence that singlet oxygen aay be involved in the production of

photocheaical lesions by blue light.

Lono-Tera Repetitive Exposures of Trained Honkevs
to Near UV Radiation and Short Wavelength Light.

These experiaents began in 1979. They were designed to
study the long-tera effects on the lens and retina of daily
exposures to near UV and short wavelength visible light siailar
to that froa the sun at sea level. The 2500 W xenon laap with
quartz optics was equipped with suitable filters and airrors to
produce two spectral bandwidths, 330-420 na corresponding
approxiaately to near UV radiation froa sunlight, and 330-490 na
corresponding roughly to the near UV plus short wavelength blue
light found in sunlight. The lens absorbs a large proportion of
the 330-420 na spectruaj less than IX of this radiation reaches
the priaate retina. On the other hand when the lens is reaoved
by cataract surgery the retina is also exposed to near UV
radiation. Approxiaatel y 27X of the light in the 330-490 na
spectrua reaches the retina in the noraal eye, i.e. lens intact.
Two experiaents with trained aonkeys were designed to study the
effects of near UV on the lens. A third experiaent was designed

14

to study the effects of blue light on the retina and the fourth
experiment was designed to study the effects of near UV on the
retina of an aphakic monkey. These experiments will be discussed
separately.

a. Near UV effects on lens with normal and dilated pucil.

The animal mith normal pupils received 971 daily exposures
to 330-420 nm radiation as of 4/13/84. The irradiated eye
receives 3mU*cm~a at the cornea for 1000 s on a daily basis, 5
days per meek. The latest examination by biomicroscope can
detect no anomalies in either the exposed or the control eye.
The pupils during irradiation have a diameter of 2-3 mm. Me have
hypothesized that perhaps the iris protects the vulnerable
equatorial region of the lens from near UV photons. To test this
hypothesis we are exposing another animal to the same spectrum
under identical conditions except that the pupils are dilated to
greater than 8 mm in diameter by the use of atropine. This
animal has received 364 exposures as of 3/15/84. No anomalies
have been detected in either eye by biomicroscopic examination.
The retinae in both animals are normal as seen with the fundus
camera. Ne plan to continue these exposure regimes with both
animals.

b. Blue light effects on the retina.

The trained monkey exposed to the 330-490 nm spectrum began
exposures in August 1981. The corneal irradiance was 5mW-cm-*
and the retinal irradiance was estimated to be 8mN*cm~*.

Periodic examinations disclosed no anomalies in either retinae or
lenses up to 371 exposures Mhen a seall but very faint patch of
depigeentation in the teaporal macula of the exposed eye Mas
noted by fundus camera examination. Fluorescein angiography was
normal in both eyes. As exposures continued this patch of
depigmentation became more prominent. After 580 exposures it
appeared to have developed into a retinal lesion, half-moon in
shape and about 400 pm x 100 pm in size. It mas decided to
sacrifice this animal for histological examination.

The animal's eyes were enucleated and he mas sacrificed on
April 20,1984. Dr. Ruffolo mill report his histological findings
in the near future. He believe that this experiment, Mhile
statistically unsatisfactory since it represents a single animal,
does demonstrate that long-term, chronic exposure of the primate
retina to blue light produces cumulative photochemical damage,
c. Near UV phototoxicity in the aohakic primate retina.

This animal had the lens removed in one eye several months
before exposures began in October 1981 to the spectral band
330-420 nm. Exposures Mere 1000 s in duration on a daily basis,
5 days per Meek. The divergence of the beam of near UV radiation
Mas adjusted to produce a 1.2 mm spot size on the retina, though
this is only approximate since the exposed eye Mas unable to
accomodate. Irradiance on the retina Mas estimated at lmN*cm-a.
Calculations based on the blue sky radiance at noon on a clear
day estimate the retinal irradiance on the aphakic human retina

• « :|| .I *»l i

with a 2 am diameter pupil to be between 2-3 mH‘cn“*. After
nearly 300 daily exposures fluorescein angiography showed
Multiple focal areas of retinal pigeent epitheliua (RPE)
depigeentation in the fundus. After 316 exposures funduscopic
examination showed two photic lesions and nueerous saall areas of
RPE depigeentation near the aacula. The aniaal was sacrificed in
Noveaber 1983. Histological analysis showed widespread RPE
abnoraalities in ^he superior and nasal paraaacular fundus. In
the superior-temporal paraaacular sample, containing the visible
photic lesions, the neural retina was lost in specimen
preparation. This was unfortunate since all of our observations
to date on near UV retinal lesions have shown severe daaage to
the photoreceptors, especially the cones. He assume the same
would have been true for this aniaal had the neural retina been
available for observation.

The inferior temporal region of the fundus was essentially
noraal. This experiaent roughly simulates daily exposures to
bright sunlight and the results indicate that the RPE of an
aphakic primate eye can be damaged by saall daily exposures to
near UV radiation.

I. Publications: 1983-1984

i. Mainster, N.A., Han, H.T. Jr. and Delori, F.C. Potenial retinal hazards:

instrument and environmental light sources. Ophthalmol. 90., 927-932 (1983).

ii. Han, H.T. Jr., Hueller, H.A., Ruffolo, J.J. Jr., Millen, J.E., Cleary, S.F.,

Guerry, R.K. and Guerry, D. III. Basic mechanisms underlying the production
of photochemical lesions in the mammalian retina. Curr. Eye Res. 2. • 165-174 (1984)

17

In Press:

i. Haa, H.T. Jr. The photopathology and nature of the blue light and near UV

retinal lesions produced by lasers and other optical sources. Chap, in ‘Laser
Applications in Medicine and Biology" Vol. 4, edited by M.L. Holbarsht, Plenua
Press, N.Y.

ii. Haa, H.T. Jr. (Chairaan), Allen, R.6., Feeney-Burns, L. , Naraor, M.F., Parver,
L.M., Proctor, P.H., Sliney, D.H. and Holbarsht, M.L. The Retinal Pigaent
Epithelial Horking Group on "The Involveaent of the Retinal Pigaent Epitheliua
in Light Daaage," CRC Press.

iii. Haa, H.T. Jr., Mueller, H.A., Ruffolo, J.J. Jr., 6uerry, R.K. and Clarke, A.M.
Ocular effects of GaAs lasers and near infrared radiation. Applied Optics.

iiii. Ruffolo, J.J., Jr., et al., Oxygen Enhanced Retinal Photosensiti vity. , Invest.
Ophthalaol. I Vis. Sci.

Abstracts: 1983-84

Ruffolo, J.J. Jr., Mueller, H.A., Haa, H.T. Jr., 6uerry, D. Ill and Guerry, R.K.
Retinal responce to chronic exposure of an aphakic eye to a 330-420 na spectral
bandwidth. Invest. Ophthalaol. & Vis. Sci. £5. , 89 (March 1984).

9. Additional Activities:

April 4-6. 1983: Dr. Ruffolo visited our laboratory and prepared speciaens for
histological and ul trastructural analysis froa 2 aonkeys after exposure to
440 na light under high arterial O2 tension.

April 8-10. 1983: Dr. Haa and Mr. Mueller attended a International Syaposiua on

Light and Oxygen Toxicity to the Eye, sponsored by the Departaent of Ophthalaology
at the University of Maryland Medical Center, Baltiaore, MD. Dr. Haa gave an
invited paper "Basic aechanisas underlying the production of photocheaical lesions
in the aaaaalian retina." Published in Current Eye Research.

April 26. 1983: Dr. Haa attended a postgraduate syaposiua on radiation hazards

associated with high technology and fiber optics coaaunication systeas, sponsored
by the Aaerican Occupational Medicine Acadeay at Hashington, D.C. and gave a paper
on "Ocular hazards associated with high technology."

Hav 1-7. 1983: Dr. Haa and Harold Mueller attended the annual aeeting of the

Associated Research in Vision and Ophthalaology (ARVO) and presented a paper
"Basic aechanisas leading to photocheaical injury of the aaaaalian retina"

July 26. 1983: Dr. Haa attended an ad hoc panel discussion on "Safety guidelines

for blue-green and ultraviolet lasers” sponsored by the Naval Medical Research and
Developaent Coaaand at Bethesda, MD.

Sept. 6-9. 19B3: Dr. Ruffolo visited our laboratory for conferences on research

progress and the design of future experiaents.

Sent, 10. 1983; Dr. Ha* attended a Syaposiua "Current Trend* in Ophthal aology-
10L Update" presented by the Richaond Eye and Ear Hospital in Richaond, VA. Dr. Haa
gave an invited lecture on "Ultraviolet effects on the eye and protective aeasures."

Sect. 25-27. 1983; Dr. Haa attended a Workshop on Long-Tera Visual Health and
Optical Radiation sponsored by the Division of Risk Assessaent, National Center
for Devices and Radiological Health of the Food It Drug Adainistration. He
chaired the Retinal Pigaent Epithelial Working 6roup Mho Mere assigned the task
of investigating light daaage to the RPE and its possible relationship to aging
and aacular degeneration of the retina. A paper evolving froa this Working 6roup
is scheduled to be published in the CRC Press in June 1985.

Oct. 6-8, 1983: Dr. Haa attended a Syaposiua on "Free Radicals in Molecular

Biology and Aging" sponsored by the Aaerican Aging Association (A6E) in Washington,
D.C.

Nov. 9-11. 1983: Dr. Ruffolo visited our laboratory and prepared speciaens for

LM and EH froa a trained aphakic aonkey sacrificed on Nov. 9, 1983 after 316 daily
exposures to the spectral band 330-420 na. This study Mas presented at ARVO,
Sarasota, Florida in Hay 1984.